Drew’s science fair was this past Friday, and he won a special award/ribbon for a “Superior” project. I’ve attached photos of he with his tri-fold board. He built/destroyed two bridges in order to prove his hypothesis, and so built a third (as seen in the photo) to show his classmates what they’d looked like.

He had to present his findings to a parent/teacher review board, and 3 of them came up to me after the fact, to say how well he presented/knew the material.

We are very proud of him, and thank you for facilitating our 5th grade science fair project!

This bridge was built by Michael in Quebec.

I have a bridge I built for a physics for engineers class I’m taking in cegep (QUEBEC). My partner and I didn’t have much confidence in it, but it blew the competition away! The design was a fairly straightforward arch as you can see. We primarily focused on keeping the weight of the bridge down. The bridge weighed in at 211 grams.

The efficiency rating worked as follows:
Weight supported by the bridge divided by the weight of the bridge squared.

This was our score. 173 KG./ (.211)squared. Our score was 3886, second place was 2100 and the rest of the competition was well below 2000. Our bridge held 381 pounds! And the lab class which we tested them in ran out of weight for us to load it with, so we couldn’t break the bridge! our teacher is building a hydraulic system to crush it next week!
~Michael.

Hey everybody once again it’s me, First Timer. I thought the one thing that would make this website even better would be some vocabulary on the parts of bridges. Here are a few terms that might help if you ever need to describe different aspects of a truss or bridge:

Arch: A structure that is curved and carries weight in a vertical manner primarily by using x-axis compression.

Beam: Horizontal structures that hold a vertical weight while not bending. Girders are multiple beams placed together and are usually the foundation of a truss.

Bridge: A structure used in aiding humans and animals in transportation over gaps, rivers, etc.

Column: The part of a bridge that connects the footing to the bottom of the bridge’s deck.

Deck: The surface of a truss or bridge that people or things drive and walk across.

Fixed Arch: A structure that is permanently in a single area/position.

Footing: The part of a bridge that is under ground level.

Member: A part in a structure, most especially a truss.

Portal: The open ends on a Through Truss, a.k.a the entrance.

Span: The length in between the inner edges of two of the “legs” of a structure.

Strut: A member that is compressive.

Substructure: Bridge parts below deck.

Superstructure: Bridge parts deck and above.

Suspenders: Tension members on the cable from the main cable to the deck of a suspension bridge.

Tie: Tension member of a truss.

Tower: A large frame holding the cables of a suspension bridge.

Truss: A stronger form of a beam or girder made with a web of members.

I hope this helps you build and describe your bridges for your classmates, students, and/or professors. Happy building everybody! If there is any other term that you don’t understand, post a comment and I will attempt to define it for you.

We run a competition here at Albury High in Australia for our Yr 12 Engineering Studies students involving max. 50 popsicle sticks, PVA wood glue and 2m of extra strong thread.  Structures have to span 400mm and are centrally loaded.  Here’s a photo of our 2010 winner which weighed in at 69 grams and held 58kgs giving an efficiency using the formula on your website if I used it correctly of around 12000!

Basswood model bridge example (built by Mr. Carlton) for students competing in the MSPE competition at MSU April 4th.

Hello! As promised, here are some pics of our bridge we entered into Jackson State Univ’s Mathematics & Engineering Fair (Jackson, MS). We were amongst what appeared to be a lot of other folks that were just as clueless as us about bridge building! This is our first effort, so a win is a win, right? It is made entirely of 1/8″ square balsa. It weighed 0.1 lbs (~45 g) & supported just under 10 lbs. The top chord is 2 1/8’s stacked on top of each other.

This next pic shows you the setup for the test: a 5 gal bucket is placed on the bridge & you slowly pour sand in until the bridge breaks. Max weight of 20kg. (my suggestion to dump a 50# bag all at once was not accepted)

We were unaware that the footing for the bridge would be 2″X2″s, & as fate would have it, they hit right in the middle of our trusses. You can see how it is flexing in between trusses along the bottom chord. This was ultimately the failure point. Otherwise, the bridge actually stayed very straight underneath the load.

Here you can see it holding up well:

In the specs for the bridges, the organizers did not specify a minimum height requirement, & 1 of the other teams took this to the extreme & built basically a pallet:

It was a great learning experience for us & has encouraged me to start a club next year where we do little beyond build bridges & towers!

Garrett Adds
Thanks for sharing! It is too bad about the unknown rule about doubling up the sticks. Your lateral bracing on the top and support for the bucket look really good. Another thing that probably would have helped is to have lateral bracing on the ends of the bridge as you look through it. This would stabilize it and help keep it from leaning or falling over sideways. You mentioned that the bridge failed because the supports (2x2s) caused a lot of shear pressure on your bottom chords.

That beam bridge is interesting, and it reminds me of a conversation I had recently with an engineer. He was saying that in real life they try to design bridges so that the mode of failure is gradual, and not sudden. It is hard to do this with model bridges, as most often they look pretty good and before you know it they just explode. But that beam bridge has enough flexibility built into it that you can definitely tell when it is having problems way before it actually breaks. Flexibility is the only plus to using hot glue. I’ve seen a bridge hold up a lot more weight simply because it did not break at the joints due to the flex in the glue than if it had used a harder glue, such as wood glue or white glue.

This album highlights the Popsicle Stick Bridge that I entered into the Seattle ASCE Younger Member Forum’s Popsicle Stick Bridge Competition in 2009. This particular entry swept all first place prizes in every category: efficiency, aesthetics, and poster. It’s 30 inches long, 11 inches tall, 5 inches wide, weighs just under 347 grams (0.77 pounds), is made out of only white birch Popsicle Sticks and Elmer’s White Glue, and it held 993 pounds before breaking (1300 times its own weight).

EDIT August 17, 2019: Album link no longer works.

I decided, for the 50th birthday of the Verrazano Bridge, to put together a model. I always loved the bridge; I lived in its shadow in Brooklyn for years and now live on Staten Island, so I use it often. Being a 2 year dad, I get little time to work on it, and when I do, my little girl sometimes “helps.” So it’s certainly not perfect, and is more of a diorama than scale model.

Most materials I already had. The towers are foam core and construction paper. The trusses are balsa wood painted with acrylic. Roadbed is oaktag with lines painted. The cables are of slightly sparkly plastic necklace wire from a craft store, the hanging cables are thread. Railings are thinly cut strips of corrugated plastic craft board. (I’m most proud of this discovery.) Elmers Glue worked throughout. The grey base is a piece of plastic siding found in my yard after cleaning out the basement after Sandy. I screwed that to a piece of wood I found on a stoop in Brooklyn. Scenery on either end is foam core, styrofoam, and acrylic paint with lichen “trees”…but I used a piece of a straw, painted white, for the lighthouse.

The necklace wire hung pretty well. The difficult part was attaching each thread (tying a knot) and getting each thread to hang straight, while maintaining the graceful curve of the cables. I had to resort to sometimes taping a penny to each cable as a weight, then putting a dot of glue between the thread and the superstructure…and cutting the penny off after it dried. I still had to redo several of them. If I made the thread too tight, it bent the main cable more sharply. A real delicate balancing game! I think next time I might just make the cables complete stiff cut-outs like some kits I’ve seen…unless I’m on a long retreat with monks and have time to meditate with thread and tweezers!

I should note that I’m also a bridge illustrator, providing custom invitations in pen and ink for Lion in the Sun paperie in Park Slope, Brooklyn. My Brooklyn Bridge…done for my own wedding…is their most popular design.

Thanks for giving me a place to post these!

We started our bridge program last year in my beginning engineering and manufacturing classes. I wanted to make a bridge that was very complicated with simple rules that required them to have to work on the mathematics of the bridge. I wanted to stress the strength of the truss design, so within the rules, I made it so other types of bridges do not work as well. Since we are a manufacturing program, I wanted to allow for more material options. I created a rule that supports manufacturing but takes away from pre-made materials. As of now, these are the rules.

The bridge rules are as follows:

1. Span is 30 inches
2. Weight limit is 200 grams
3. All materials are allowed except:
   1. pre-hardened glue (example: no plywood, but creating plywood is acceptable).
   2. contained gases
4. I will supply 3/16 wood sticks of varying materials (right now: fir, mahogany, spruce, cedar). Material outside of this is on your own to get.  (balsa is outside of our budget).
5. The bridge must hold our 3 inch by 5 inch square that houses the eye bolt and carabineer. The hanger must be within 3 inches of the center of the span.

The students have access to 3D printers, Solidworks, welders, metals, plastics, wood, machining tools, CNC routers, and even composites.

Due to the manufacturing nature of my program, some groups head straight for the most technological solutions and find struggles early and often. 3D printing in today’s world seems like a logical solution to solve this problem, but it is both time consuming and heavier than they think. A few groups have played with carbon fiber and I believe that there are some amazing solutions available in composites for this assignment, these students are using the material in odd ways, which leads back to this assignment is more about engineering than manufacturing. That said, the students that spend the most time manufacturing quality joints do really well.

I push groups to design a truss style bridge out of 3/16 shop made sticks. Then use paper gussets glued with Elmer’s glue. We have learned that the gussets do really well, but they need clamping.  We discovered that binder clips make the best “Bridge Clamps.”

Most of our success comes from arch type bridges and truss type bridges. Arches are made easily with 2-4 bridge sticks glued into an arch (laminated). Some of our bridges have held 120 pounds. To achieve success in my grade book, they should strive for 70 pounds. This may not seem like a lot, but the span is impressive. I felt like the common 16 inch bridges could find some success with just a stick across the span. We found that a 32 inch metal beam bridge made that falls under 200 grams limit held about 10 pounds.

My only issue with balsa is cost, in order to run a classroom program with balsa, I would have to spend upwards of 600-800 per year in balsa. A group did go out and purchase balsa and found similar results to our fir wood at a fraction of the cost.

This is how I make the sticks. I find fairly straight grained VG fir and resaw the boards on the bandsaw to 3/16 of an inch. Then I glue the ends of the resawn wood together to act as a form of clamp. Then I resaw the glued boards the other direction. This allows me to make them in bulk both quickly and cheaply. I generally make them at 36 inches as most bridges are 32 inches and with an arch it is easy to get to 36 inches. Students have done experiments with different wood species to varying success. One group discovered that cedar was much lighter, but had terrible compression strength. They used cedar on the tension members and fir on the compression members.

You can visit our class at www.penguinmanufacturing.com or follow us on instagram @penguinmanufacturing